Telephone system



, TELEPHONE SYSTEM Filed April 22, 1929 2 Sheets-Sheet l ---w ,55 4\ 40 LOCAL BUSY l 20 62 l r ri -ET"? (Lfi &

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TELEPHONE SYSTEM- Filed April '22, 1929 2 Sheets-Sheet 2 BB 54 1 2%. 39 l M ,7? 7| 74 v 56 wa g1 D l g V 25 E \Qfi fnuanfrs- Rs inald T glur' Char-'12s Edmund Bill:

Patented Mar. 31, 1931 warren srArEs PATENT orrics REGINALD TAYLOR, OF LIVERPOP-L, AND CHARLES EDM'UITD BEALEJ, OF LONDON, ENG- LAND, ASSIGNOBS, TO ASSOCIATED TELEPHONE AND TELEGRAIEI-I COMPANY, OF CHICAGO, ILLILTOIS, A COR-PGRATION OF DELAWARE TELEPHONE SYSTEM:

Application -fi1ed April 2. I

The present invention relates to telephone systems andis more particularly concerned with finalselectors or connectors or the socalled offering type, that is, switches which are provided to enable a trunk operator to establish telephone connection with a busy subscriber for the purpose of offering the said subscriber a trunk call.. It is a well established practice in large telephone syste1ns,"to install a separate train of switches for trunk offering facilities and the purpose of the pres: ent invention is to provide a universal switch whereby ordinary calls and trunk offering calls may be completed'ever the same train of switches.

It will be appreciated that on an offering call'means are provided whereby the switch will cut in on a connection be-tv een two ordinary subscribers.

According to one featureof the invention, ringing current is connected to the required subscribers line, when both parties havecleared in response to an offering call and two methods of accomplishing this feature are shown in the attached drawingsyl ig. 1'

illustrating a method whereby ringing 1S" automatlcally connected when both parties clear and Fig. 2 showing a method of allow- 1 ing the trunk operator to controlthe extension of ringing current. ItNvill be noticed" that whichever method is used the called party may be rung without the necessity. for the operator to reset up the connection.

A further feature of the inventionis,that

in the event of a trunkoperator calling a subscriber who is already engaged on a trunk call, the switch is so arranged that it will not cut in and a special trunk busy back tone 1s 40 1 extended to the calling trunk operator.

These features will bebetter'appreciated from the'following description, which should be taken in conjunction with the'accompanying drawings oi" which Fig. 1 shows a-final selector or connector switch o-fsubstant'ially known type, arranged by the inclusion of suitable relays, to be used indiscriminately on trunk or ordinary calls, and Fig; 2 which shows asimilar switch in which the fourth wiper hasbeen dispensed with, and the ap- 1929Q$eria1 no. 356,910, and inGreat Britain June 5, 1928.

plication of ringing on an offering call is controlled by the trunk operator.

Referring now particularly to Fig. 1, when a' subscriber initiates a call by removing his receiver and dialling the necessary digits, he will operate the usual trunk switches which may be of the general type disclosedin sociated with armature 17, conductor 15, call mg loop, conductor 10, resting springs associated with armature 16, upper winding of relay A to battery. The operation of relay A energizes relay B, which in turn earths the release trunkconductor 11 over armature 22 and resting contacts of the off-normal springs N, and prepares the impulsin'g circuit at its armature 24.

When the first vertical impulse is received, relay A releases thereby extendingearth at armature 21, armature 24: and front contact, resting contacts of Off no-rmal springs N, winding of low resistance relay C in series wit the vertical magnet'V to battery, thereby causing the sha'it'and wipers to be raised to the first level. The oii normal springs N op crate on the first vertical step so that tiiie neXt ve-rtical'impulse will follow the circuit, earth at'arniature 21, armature and front contact, operated off-normal springs, armature 26 and'fron't contact, winding ot relay C in series with the vertical magnet V to bat tery. It will be seen from the drawing that relays B and C are equipped with copper slugs so that they'will accordingly remain opcrate-d while relay A is impulsing to maintain the circuit to the vertical magnet. The operation of the oft-normal springs N extends earth at armature 22 ofrelay B through he lower winding of the diiiferentially wound relay DR to battery, and also connects the upper winding in series with the release trunk conductor 11 which extends to battery through the switching relays of preceding se lectors of the switch train. Relay DR however remains unoperated due to the opposition of the current flow in its windings. At the completion of the dialled vertical impulses, relay C will release so that the first rotary impulse will follow the circuit, earth at armature 21, armature 24, operated oil'- normal springs N, armature 2(5 and back contact, armature 39 and back contact, winding of relay E to battery, and parallel thereto, armature 52 and windin of rotary magnet to battery, thereby causing the shaft and wipers to be rotated into contact with the first set of bank contacts of the selected level. Relay E it will be noted is also equipped with a copper slug so that it holds during impulsing, and whilst it is operated, an alternative path is provided for the rotary impulse via its armature 59, and a circuit is also prepared for the busy relay G. Magnet R operates in step with the rotary impulses to set the wipers on the bank contacts of the wanted subscriber.

Assuming now that the called subscriber is busy, wiper 57 will encounter earth and before the slow relay E restores the following circuit will be completed: earth at wiper 57, armature 45 and front contacts, back contact and armature 42, win-ding of relay G to battery. Relay G operates and, when relay E restores, completes a locking circuit for itself as follows: earth, armature 22, armature 37 and front contact, back contact and armature 29, resting springs of armature 45, armature 42, winding of relay G to battery.

Moreover, the operation of relay G disconnects the impulsing circuit to the rotary magnet at armature 39 to prevent any further impulses being transmitted to the rotary magnet and further extends busy back tone over the following circuit: conductor BB, front contact and armature 40, back contact and armature 30, armature 47 and back contact, via the talking condenser and conductor to the calling subscriber to inform him that the number dialled is busy. Should however the number dialled test free, viper 57 will not find earth, and, when relay E releases at the completion of the series of retary impulses, battery via the ca led subscribers cut-off relay will be connected via wiper 57, armature 45 and back contact, upper winding of relay H, back contact and armature 37, armature 22 and front contact to earth, thereby causing the relay H to operate its armature so that lower winding becomes energized over a circuit extending over armature 53 and armature to earth, and the relay then operates all its armatures. Immediately relay H operates fully, the calling subscriber will be busied from earth via armature 51, and ringing current will be extended over the following circuit: earth and ringing current over conductor RT, upper winding of relay F (which is insensitive to ringing current) back contact and armature 32, front contact and armature 48, wiper 55,

called subscribers loop, Wiper 58, armature 54 and front contact, armature and back contact, resistance 20, conductor 62 to battery; thereby causing the called subscribers bell to ring. Furthermore, a ring-back tone is supplied to the calling subscriber over a leak path to the main ringing circuit, from armature 49 via a ring back condenser and talking condenser to conductor 10, to indicate to the calling subscriber that the called subscribers bell is being rung.

When the called subscriber removes his receiver to answer the call, relay F operates its armature 33, by direct current flow around the ringing circuit previously described, thereby completing the energizing circuit of the lower winding to earth at armature 25 so that the relay will then operate fully, and disconnect the ringing circuit at armatures 32 and 35. Relay D will now operate over the following circuit: earth, lower winding of relay D, front contact and armature 35, front contact and armature 54, wiper 58, called subscribers loop, wiper 55, armature 48 and front contact, armature 32 and front contact, winding of relay D to battery, thus reversing the battery feed to the calling loop at armatures 16 and 17, for metering or supervisory purposes. It will be seen that the release of the switch is dependent upon the last part, i. e. both relays B and D must release to complete the release magnet circuit as follows: earth, armatures 21, 24 and 18, working contacts of off-normal springs N, winding of release magnet RM to battery.

Consider now the case in which the trunk operator desires to olfer a call to one of two busy subscribers to which a connection has been extended over a toll trunk such as that disclosed in United States Patent to icks, No. 1,593,737 of July 27, 1926 and the connector shown in Fig. 1. The operator sets up the connection in the usual way by dialling the number of the called subscribers line. hen the connector is seized by the preceding selector, relays A and B will be operated over the selector train as previously described, and earth will be extended over conductor 11 by the relay group associated with the incoming trunk. When off-normal springs N operate after the first vertical step, a circuit is completed as follows: earth, armature 22, operated oif-normal springs N, lower winding of difierentially wound relay DR to battery. whereupon the relay operates since its upper winding is now short-circuited from earth fed forward over conductor 11 on one side, and earth via armature 22 on the other side. Relay DR upon operating, short-circuits its upper winding directly at armature 66, to ensure that the relay DR remains operated in spite of any fluctuations of the short-circuiting earth fed forward over conductor 11.

Referring now to the call in progress, it will be remembered that when the final selector wipers arrive on the busy contacts, relay G will be operated from earth on wiper 57, and when relay E releases after its slow period a locking circuit will be established for relay G as follows: earth, wiper 57, front contact and armature 38, front contact and armature 29, resting springs associated with armature 45, back contact and armature 42, winding of relay G to battery. A speaking circuit is thereby completed for the offering trunk operator, the upper speaking conductor being extended to wiper over armatures 64, 36 and 27, the lower speaking conductor being extended to wiper 58 over armatures 31, 41 and 65.

The trunk operator is then able to speak over the circuit described, and assuming that the call offered is accepted, she will then request both parties to hang up their receivers thereby causing the following circuit changes to ensue.

WVhen both the calling and called parties have cleared, the associated final selector will release, thus causing the guarding earth on wiper 57 to be removed so that the holding circuit of relay G- is opened. Relay G releases and the following circuit is completed: battery via the called subscribers cut-off relay, wiper 57, armature 45 and back contact, upper winding of relay H, back contact and armature 87, armature 22 to earth, thereby causing relay H to operate its light armature 53, to complete a circuit for its lower winding from earth atarmature 25. Relay H then operates all its armatures and again applies ringing current to wipers 55 and 58, and ringing current is fed to the desired subscriber, after which the subsequent train of opera tions is as previously described. It will be noticed that upon the operation of the differential relay DR, earth is extended via armatures 46, 28 and 63 to wiper 56, and assuming that another operator endeavours to offer a call to a subscriber who is already engaged on Trunks, the circuit arrangement of the calling switch is such that the cut-in feature is rendered ineffective. At the completion of the rotary impulses and before relay E releases, earth will be extended over wiper 56 of the calling final selector, armature 63 and front contact, armature 28 and front contact, armature 46 and front contact, winding of relay T to battery, thereby causing the relay to operate. When relay E releases after its slow period, relay T will lock operated from earth at armature 25, armature 43 and front contact, resting springs of armature 46, winding of relay T to battery. The operation of relay T, disconnects the circuit of relay G at armature 42 so as to prevent the speaking conductors being extended at armatures 36 and 41, and at armature 44 extends a trunk busy back tone to the calling operator over conductor TB, front contact and armature 44, front contact and armature 30 and armature 47 and In the event of the calling party failing to restore his receiver after a reasonable period at the completion of a call, relays A, B and F will be maintained operated and supervision is provided from earth at armature 34, armature 19 and back contact to conductor 13;

if the called party fails to restore his receiver relay D will be maintained operated and supervision is provided from earth at armature 21, armature 24 and back contact, armature 18 and front contact, to conductor 18, causing a delayed alarm scheme to be set in operation.

Referring now to Fig. 2, when an ordinary subscriber seizes the connector, relays A and B will operate, and, upon the reception of the first vertical impulse, relay A releases, thereby extending earth via armature 24, armature 25 and front contact, resting contacts of elf-normal springs N, armature 61 and back contact, winding of vertical magnet V to battery, thereby causing the shaft and wipers to be raised to the first level. A parallel circuit is also completed for relay C over armature 60 and its back contact. The off-non mal springs N are operated on the first vertical step so that the subsequent Vertical impulses will follow the circuit, earth via armatures 24 and 25, operated off-normal springs N, armature 27 and front contact, armature 61 and back contact, winding of vertical magnet V to battery.

It will be noticed that both relays B and 0 remain operated during impulsing due to the copper slugs surrounding their cores. The operation of off-normal springs N, completes a circuit to the lower winding of the difierential relay DR from earth at armature 23, but since the upper winding is already energized from battery via the switching relay of the preceding selector, the relay DR remains inoperative as mentioned in the previous description. At the completion of the dialled vertical impulses, relay C will release so that the rotary impulses will follow the circuit, earth via armatures 24 and 25, operated off-normal springs N, armature 27 and back contact, back contact and armature 42, winding of relay E to battery, and in parallel therewith, armature 68 and back contact, inding of rotary magnet R to battery, thereby causing the shaft and wipers to be rotated into engagement with the bank contacts corresponding to the subscriber dialled. Relay E it will be noticed is held during impulsing, due to the copper slug surrounding its core, thereby providing an alternative circuit at its armature 59 should relay G operate, while wiper 7 3 is passing over busy earthed contacts.

Assuming now that the called subscriber is busy, when the connector wipers arrive on the busy contacts, wiper 73 will encounter earth, and before the slow releasing relay E restores the following circuit will be completed: earth at wiper 73, resting springs associated with armature 67, armature 57 and front contact, winding of relay G to battery, thereby causing rela G to operate and complete a locking circuit for itself when relay E restores. The operation of relay G prepares various circuits which will be described later, and further extends busy back tone over the following c'rcuit: busy back tone conductor BB, armatures lo, and (52, via the transmission condenser and conductor 15 to the calling subscribers instrument to inform him that the number dialled is busy.

Should however, the number dialled test free, wiper 73 will not encounter earth, and when relay E releases at the completion of the dialled rotary impulses, battery via the called subscribers cut-oil relay will be extended over wiper 78, resting contacts associated with armature 6'7, armature 57 and back contact, upper winding of relay H, back contact and armature l0, armature 23 to earth. Relay H thereupon operates its light armature 69 so that its lower winding becomes energized and the relay then operates all its armatures. The complete operation of relay H completes the following circuit: earth, ringing tone conductor R'l, upper winding of relay F, armatures 51, 3G and (33, wiper 72, called subscribers loop, wiper T4, armatucs 71, 39 and 56, ringing resistance and conductor 77 to'battery, thereby causing the called subscribers bell to ring, whilst at the same period a. ring back tone is supplied to the calling subscriber, over a leak path via armature (i-l. From this point the sequence of operations is similar to those described in connection with Fig. 1, and will be readily apparent.

Referring now to the case when a trunk operator desires to oller a call to one of two busy subscribers, relays A and B will be operated over the calling loop, and earth will be extendml forwards over conductor 11 by a relay wl i h is connected in series with each incoming trunk thereby short-circuiting the uppe winding of the lillerential relay DR so that it will now operate over its lower winding when the -normal springs are operated. It will be recalled that during the transmission of the rotar impulses, relay E is operated in parallel with the rota y nagnet ll, and since relay DR is now operate-(l, relay C will again operat over t l ll l owing circuit: earth, armature front contact and armature 33, front contact and rniature GO, winding of relay l to battery; relay C prepares a circuit at its armature 28 for relay T which will be dealt with later. When the wipers of the connector arrive on the busy contacts, relay G will be operated as previously mentioned, that when relay E restores a locking circuit is completed as follows: earth at wiper 7S, armatures 41, 31 and 17, resting contacts associated with armature 57, winding of relay G to battery. \Vhen relay C releases due to its disconnection at armature of relay E, earth is extended by way of armatures 29, 34: and l?) to the winding ot relay RC, thereby causing the relay EC to operate and lock up, thus completing the following transmission circuit for the oli'ering trunk operator, wiper 72, armature 50, transmission condenser, conductor 10, operators transmission circuit, conductor 15, transmission condenser, armature to Wiper 74. he trunk operator is thus able to speak over the foregoing circuit, and assuming that the offered call is accepted, she will then request both parties to hang up their receivers in order that she may recall the wanted subscriber. It should be mentioned here that consequent upon. the joint operation of relays G- and RC a circuit is completed for relay D as follows: earth, lower winding 0t relay 1), aru'iatures 553 and 3, upper winding of relay D to battery, thereby causing the relay to operate, and at its armatures 16 and 17 reverse the current flow around the calling loop, for the purpose of supervision. lVhen both subscribers have cleared in response to the operatofs request, the associated connector will release thus causing the guarding earth on wiper 73 to be removed, so that the holding circuit of relay G is disconnected. The circuit of relay D will then be broken at armature all and it will release, thereby restoring the direction of current flow in the calling loop in order to provide the neces sary supervision to the calling operator to the effect that both subscribers have cleared.

It will also be noticed that upon the release of relay Gr, battery via the called subscribers cut-ofl' relay is extended over the following circuit: wiper 7S, resting springs of armature 67, armature 57 and back contact, upper winding of relay H, armature l0, armature 23 to earth, thus causing the relay to operate its light armature 69 and complete a circuit for its lower winding, whereupon the relay operates fully and prepares various circuits which will be explained later.

When the calling operator observes from her supervisory apparatus that both subscribers have cleared, she operates the ringing key associated with her cord circuit, thus causing the ringing relay HR to operate from ringing current over conductor 10, winding of relay RR, condenser 14, armature 54, con ductor 15 to the other side of the ringing teed. Relay RR opens its springs 20 so that the locking circuit of relay RC is broken and it releases thereby completing the ringing circuit at armatures 51 and 56, after which the subsequent operations are as previously described. It will be noted that upon the operation of both relays B and DR- as in ill) aztrunk. call, direct earth is disconnected at armatures '22and 30, but earth via. resistance 12is connected over. armature .67 .and wiper 73to the private'bank contacts. Ifanother operator endeavours to offer a call at this period, the followingv circuit operations will ensue. When the wipers of the calling switch arriveon thebusy contacts, relay'G will be operated as previously explained sothat it looks up" to the resistance earth on wiper 73: when relay E releases at the completion oi the rotaryimpulses, a circuit is completed. as follows: earth, armature 26,.upper-winding of relay T, armatures l4, 28 and 57, -resting springs of armature 67, arm'atures 41,31 and 47, resting springs of armature 57, winding of relay. G to battery, whereupon. relay T operates its light armature 48 and the extra current flow via the resistance conveniently wound on the relay T enables it to fully operate. The locking circuit of relay G is therefore broken at armature 47 so that it releases, thus allowing trunk busy back tone to be extended over the following circuit: trunk busy conductor TB, armatures 49, 35 and 62, transmission condenser via conductor 15 to the calling loop, thereby indicating to the offering operator that the desired subscriber is already engaged on a trunk call.

Last party release is incorporated in the switch in similar manner to that shown in Fig. 1 and certain supervisory apparatus is brought into operation should either subscriber tail to clear after a predetermined period.

What we claim as new and desire cure by Letters Patent is:

1. In a telephone system in which local and toll connections are set up in part over the same switch train and in which holding aotential is supplied from the last switch of the train in local connections and from'the first switch of the train in toll connections, a connector switch operating as the final switch of the train in either connection, and means in the connector for adapting the same to operate as a local or a toll connector dependent upon the source of holding potential in the connection.

2. In a telephone system in which local and toll connections are set up in part over the same switch train and in which the holding conductor extending through the switch train is grounded at the final switch of the train in connections of both classes and also at the first switch of the train in toll connections, a connector operating as the final switch of the train in connections of both classes, and means in the connector for adaptto se- A ing the same to operate as to toll connector or as a local connector dependent on the pres ence or absence of ground on the test conductor at a preceding switch of the train.

3. In a telephone system, a connector operating as the final switch of a train in either local or toll connections, means in the connector for applying a holding potential to the test conductor extending through the switch train, and means inthe connector responsive when a similar potential is applied to said test conductor at a preceding switch in the train for adapting the connector for toll operation.

.4. In a telephone system, a connector operating as the final switch of a train in either local or toll connections, means in the connector for applying a holding potential to the test conductor extending through the swi ch train, and a relay in the connector connected in said test conductor operative when a similar potential is connected to said test conductor at a preceding switch of the train for adapting the connector for toll operation.

5. Ina telephone system, a connector operating as-the final switch of a train in'either local or toll connections, a test conductor extendingthrough the switch train and terminating in the connector, a diiferentially wound relay having one winding energized in alocal, circuit-when the connector is in use and the other winding connected in said test conductor, and means in the connector for connecting a source of current to said test conductor to energize said other winding of therelay in series with the switching relays or" preceding switches to prevent the operation of the relay in local connections.

-6.' -.In a telephone system, a connector operating as the final switch of a train in either local or toll connections, a test conductor extending through the switch train and terminating in the connector, means in the connector forz connecting a holdingpotential to saidconductor, and a differentially wound relay having one winding energized in a local circuit and the other winding connected in said test conductor for controlling the mode of operation of the connector, said other winding being energized by said holding potential in series with the switching relays of preceding switches in local connections to render the relay inoperative, and shunted by a similarholding potential applied to said test conductor by a preceding switch of the train in toll connections to render the relay operative.

7. In a connector switch accessible over a trunk comprising two talking conductors and a test conductor, said switch being normally adapted to operate as a local connector, arelay for adapting the switch to operate as a toll connector, and means for connecting saidrelay to said test conductor responsive to the off-normal operation of the switch.

8. Ina connector switch accessible over a trunk comprising two talking conductors and a test conductor, said switch being normally-adapted to operate as a local connector a relay having a short circuited winding connected to. saidtest; conductor foradapting the switch to operate as a toll connector, and means for opening the short circuit for said 'inding responsive to the ofi-normal opera tion of the switch.

9. In a connector switch accessible over a trunk comprising two talking conductors and a test conductor, said switch being nornally adapted to operate as a local connector, a relay for adapting the switch to operate as a toll connector, and means responsive to the oil-normal operation of the switch for rendering said relay controllable over said test conductor.

10. In a connector switch accessible over a trunk comprising two talking conductors and a test conductor, a differentially wound relay, a local circuit in the switch for one winding of the relay, a circuit extending to a preceding switch over said test conductor for the other winding o1 the relay, and means responsive to the oil-normal operation of the switch for completing both of said circuits.

11. In a connector switch accessible over atrunk comprising two talking conductors and a test conductor, said switch being normally adapted to operable as a local con nector, a. relay having awinding connected in said test conductor for adapting the switch to operate as a toll connector, oil-normal contacts short-circuiting said winding when the switch is in normal position, and contacts on said relay for short-circuiting said winding when the relay is operated.

12. In a combination toll and local connector for extending calls to subscribers lines, a wiper for applying a guarding potential to the test contact of a subscribers line to which a local or toll call is extended, and a second wiper for applying a guarding potential to an auxiliary test contact of a subscribers line to which a toll call is extended.

13. In a combination local and toll connector, a relay for testing the busy or idle condition of a called line, a second relay for testing toll busy or local busy condition oil said line, and separate test wipers for connecting said relays to the test contacts of the called line.

14:. In a combination local and toll connector, a busy test relay and a discriminating test relay connected to the test contacts of a called line over separate test Wipers, said first relay energizing when the called line is busy in either a local or a toll connection and said second relay energizing only when the called line is busy in a toll connection, contacts on said first relay for connecting up a local busy tone, and contacts on said sec ond relay for connecting up a toll busy tone.

1;). In a telephone system in which local and toll connections are set up in part over the same switch train and in which holding potential is supplied from the last switch of the train in local connections and from the first switch of the train in toll connections, a connector switch operating as the final switch of the train in connections of either class, means in the connector I or adapting the same to operate as a local connector or as a toll connector dependent on the source of holding potential in the connection, and means in the connector for completing a talking connection to a locally busy called line when the connector is used in a toll connection.

In testimony whereof we the said REGINALD TAYLOR and CHARLES EDMUND BEALE have signed our names at Liverpool this 25th day of March, 1929.

REGINALD TAYLOR. CHARLES EDMUND BEALE. 

